Currently, IEEE802.15.4 standard develops a Media Access Control (MAC) layer protocol, which provides communication solutions for short range wireless networks including wireless communication networks such as wireless personal area network (WPAN) and wireless sensor network (WSN), etc. The transmission range specified by the MAC layer protocol is about 10 meters which is a typical WPAN range.
The main features of WPAN are low rate, low power consumption, low complexity and having numerous wireless nodes. WPAN has potential applications in the field of sensors, remote control toys, smart badges, remote controllers and family automations, etc. The solution provided by the IEEE802.15.4 has both low power consumption and low complexity. Therefore, battery life may last several months or even several years.
IEEE802.15.4 utilizes a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) media access mechanism in a Contention Access Period (CAP). Currently, in a network with slotted CSMA/CA mechanism, a coordinator may send a beacon to all sensing devices. For a device requiring data transmission, it may send a request to the coordinator for data transmission. Since only one device can transfer data at one time, all the devices which intend to transfer data may contend for the usage of transmission media with a slotted CSMA/CA algorithm.
The contention for the usage of transmission media includes the following process. All the devices which intend to transfer data need to monitor if the current wireless transmission media is being used by other device. If a current wireless transmission media is being used by other device, the device may generate a random backoff period to wait for a next channel sensing. If the current wireless transmission media is idle, the device may start to transfer data. Such process is called a non-persistent CSMA mechanism.
The coordinator needs to send an acknowledgement frame to the device after receiving a data frame from the device. If the device has not received the acknowledgement frame within a timeout period (the maximum period for the device to wait for the acknowledgement) after the device completed the transmission of the data frame, it means that the transmission fails.
To evaluate the CSMA/CA performance of networks with contention access mechanism, such as WPAN or WSN, a throughput of the network must be determined. In this way, network access can be optimized in a network according to a corresponding requirement for network performance so as to enhance the probability of a successful network access, ameliorate the network performance, and thus optimize the network throughput and achieve a desired network throughput.
Currently, in a short range wireless network such as WPAN or WSN, the network throughput is computed in accordance with CSMA/CA mechanism in IEEE802.11 standard. Specifically, a Markov model can be employed to compute a conditional probability of data transmission given a backoff state of a device. Thus, a derivation formula of the network throughput can be obtained.
However, in the implementation of invention, the inventor discovers that the mechanism of the short range wireless network such as WPAN or WSN is different from CSMA/CA mechanism of IEEE802.11. Specifically, the differences are listed below.
(1) The short range wireless network such as WPAN or WSN does not employ virtual carrier-sense mechanism so as to reduce power consumption of network devices.
(2) Request-to-send (RTS)/clear-to-send (CTS) is not employed in short range wireless network. The reason is that a single node in the short range wireless network has a low transmission rate and the data packet in transmission is not large. The loss due to the contention has less impact than does the loss due to the contention in terms of the IEEE802.11. Therefore, there is no need to arrange RTS/CTS.
(3) IEEE802.11 employs a slotted CSMA/CA, while the short range wireless network such as WPAN or WSN may employ two mechanisms, slotted and unslotted CSMA/CA. The slotted CSMA/CA frame is arranged with a dedicated contention slot while the unslotted CSMA/CA mechanism is not arranged with a contention slot.
Furthermore, the inventor discovers that if the short range wireless network such as WPAN or WSN employs CSMA/CA mechanism of IEEE802.11, it obviously does not take into consideration the intrinsic characteristics of CSMA/CA in the short range wireless network such as WPAN or WSN. Therefore, the computed network throughput may see relatively a large error, which might not be able to reflect truthfully the CSMA/CA performance in the short range wireless network such as WPAN or WSN. This might further causes inability to optimize the network access based on an accurate network throughput, which may decrease the probability of successful network access and at the same time overly increase the power consumption of the network device. Moreover, the computation process for a successful clear channel assessment (CCA) probability and a throughput is cumbersome.